Up to the present time, there has generally been employed an electrophotographic process for the production of a lithographic printing plate precursor comprising subjecting the photoconductive layer of an electrophotographic lithographic printing plate precursor to uniform static charge, to imagewise exposure and then to liquid development with a liquid toner to obtain a toner image, then fixing this toner image and processing with an oil-desensitizing solution (etching solution) to render hydrophilic a non-image area free from the toner image.
As a base for the lithographic printing plate precursor, a paper which has previously been rendered electroconductive, etc. is used, but this paper base is penetrated with water, resulting in bad influences on the printing durability or photographic properties. That is, the paper base is penetrated with the above described etching solution or dampening water during printing and expanded so that the photoconductive layer sometimes separates from the paper base to lower the printing durability, sad the moisture content of the paper base is varied with the temperature and humidity conditions in carrying out the above described static charge or imagewise exposure so that the electric conductivity is varied to affect unfavorably the photographic performances. Furthermore, if the water resistance is insufficient, wrinkles occur during printing.
In order to solve these problems, it has been proposed to coat the one or both surfaces of a support with, for example, an epoxy resin or ethylene-acrylic acid copolymer having water resisting property (Japanese Patent Laid-Open Publication Nos. 138904/1975, 105580/1980 and 68753/1984) or to provide with a laminated layer of polyethylene or the like (Japanese Patent Laid-Open Publication Nos. 57994/1983).
Furthermore, a layer provided as a back coated layer on the opposite surface to a surface of a support having a photoconductive layer (also called "top layer" or "printing surface") is called a back layer, and various improvements have been made as to a composition for forming the back layer for the purpose of not only imparting water resistance thereto, but also maintaining various functions.
The inventors have developed and proposed, as a process for developing an electrophotographic lithographic printing plate precursor, a liquid development method by the so-called direct electron injection system, as disclosed in Japanese Patent Laid-Open Publication No. 26043/1989, which method comprises using a conductor instead of an electrode at the opposite side of a printing surface and effecting development while directly feeding electrons to the back side of a base from this conductor, whereby the prior art system of passing a master through a developing liquid flowed between electrodes is substituted.
As an improved technique, the inventors have further proposed a precursor comprising a base having polyolefin laminated layers on both the surfaces of the base, provided with, as a back layer, a layer having a surface electric resistance of at most 1.times.10.sup.10 .OMEGA. and a larger friction resistance than the polyolefin laminated layers, whereby to render correct winding and fixing of the printing plate, to prevent slipping in printing, to carry out favorably electrophotographic printing plate making and to render possible developemnt by the direct electron injection system (Japanese Patent Laid-Open Publication No. 84665/1990).
In addition, the inventor have proposed a precursor comprising an under layer and a photoconductive layer provided on the surface of a base and a back layer on the back surface thereof, the under layer having a surface resistivity of 1.times.10.sup.8 to 1.times.10.sup.14 and the back layer,having a surface resistivity of at most 1.times.10.sup.10, whereby a uniform image can be formed by any develpment method of the prior art and the direct electron injection system precisely, favorably and rapidly without occurrence of pinholes as a solid image, and a development method thereof (Japanese Patent Laid-Open Publication No. 132464/1990).
Since a lithographic printing plate precursor is ordinarily wound in the form of a roll, a back layer and a printing surface (top layer) are brought into contact with each other and a composition for forming the back layer, for example, a water resistance improver is tranferred to the top layer. If the water resistance improver adheres to a toner image-free area (non-image area), there arises such a problem that stain occurs on a print (called printing scum by rubbing). When the amount of the water resistance improver in the back layer is decreased so as to prevent the rubbing stain, the water resistance (water proof property) is naturally lowered so that wrinkles occur during printing and further printing is impossible. That is, it is difficult to satisfy both the requirements, i.e. preventing the rubbing stain and maintaining the water resistance (preventing wrinkles during printing).
For the back layer is required a function to ensure printing adaptability or operativeness, such as tendency of adhering to a printing drum (fitting property) and not slipping from the printing drum in addition to the above described two functions.
Therefore, it is an object of the present invention to provide an electrophotographic lithographic printing plate precursor having a good performance for the printing scum by rubbing and tendency of less occurrence of wrinkles during printing, and being capable of satisfying the printing performances such as fitting property and tendency of hardly slipping off and printing a number of good image prints.
It is another object of the present invention to provide an electrophotographic lithographic printing plate precursor capable of being applied to both development of the ordinary electrophotographic printing plate and development of direct electron injection system and further satisfying the above described prevention of the printing scum by rubbing and printing performances.